MODELING RHEOLOGICAL PROPERTIES OF SOME MOLASSES-TAHIN BLENDS
Dlshad Abdalla Mohammed
MSc THESIS
Chemical Engineering Department Supervisor: Prof. Dr. Fethi KAMIŞLI
T.C.
FIRAT UNIVERSITY
THE INSTITUTE OF NATURAL AND APPLIED SCIENCES
MODELING RHEOLOGICAL PROPERTIES OF SOME MOLASSES-TAHIN BLENDS
MSc THESIS
By
Dlshad Abdalla Mohammed (151118105)
Study Field: Chemical Engineering Program: Unit Operation and Thermodynamics
Supervisor: Prof. Dr. Fethi KAMIŞLI
Submitted Date: 23.07.2018
I
ACKNOWLEDGEMENTS
This work would have not been possible without assistance and guidance of number of individuals and their courage who by one way or another appreciably contributed to accomplishment of this thesis.
At the starting, I would like to precise my significant and fair gratefully to my supervisor Prof. Dr. Fethi KAMIŞLI not as it were for his cherished direction, coordinate offer assistance, back and support but too for his parental care amid my residency in Turkey. I moreover, would like to communicate my profound appreciation to all staff of chemical designing office in Firat University for their help and their special classy treatment with me during my study.
I cheerfully thank Prof. Cevdet AKOSMAN who helped me, thanks to Prof. Nurhan ARSLAN who helped me to integrate into Turkish society and much obliged to Research Assist. Ercan AYDOĞMUŞ for giving me hands in my work, all of that made a difference me to communicate and be commonplace with other understudies and cadres of the division and feel as be at my home.
Finally, I must express my very profound gratitude to my parents and to my wife, for providing me with unfailing support and continuous encouragement throughout my years of study and through the process of researching and writing this thesis. I want to dedicate this work to my wife and both my little daughters Lana and Wara. Thank you.
II TABLE OF CONTENTS ACKNOWLEDGEMENTS ... I SUMMARY ... IV ÖZET... VI LIST OF TABLES ... X 1. INTRODUCTION ... 1
2. OVERVIEW AND LITERATURE SURVEY ... 3
2.1. Molasses ... 3
2.1.1. Preparation of Date Syrup ... 3
2.1.2. Fresh Mulberry ... 4
2.1.3. Fresh Grapes ... 4
2.1.4. Carob Molasses ... 5
2.2. Sesame Paste ... 7
2.3. Molasses/Sesame paste mixtures ... 8
3. RHEOLOGY AND FLUID FLOW MODELS ... 9
3.1. Rheology ... 9
3.2. Importance in the Food Industry ... 9
3.3. Rheological Behaviors of Fluid Flows ... 9
3.3.1. Newtonian Fluids ... 10
3.3.2. Non-Newtonian Fluids ... 10
3.3.2.1. Time Independent Fluids ... 11
Bingham Plastics ... 11
Power-law Fluids ... 11
Herschel - Bulkley Fluids ... 13
3.3.2.2. Time-Dependent Fluids ... 13
Thixotropic Fluids ... 13
Rheopectic Fluids ... 14
3.4. Effective Variables on Viscosity ... 15
Effect of Temperature ... 15
Effect of Concentration ... 15
The Combined Effect of Temperature and Concentration ... 16
3.5. Impact of Concentration on Activation Energy ... 16
4. MATERIALS AND METHODS ... 17
4.1. Materials ... 17
III
4.2. Rheological Analysis ... 18
4.2.1. Measuring of Rheological Behavior ... 18
4.2.2. Statistical Analysis ... 19
5. RESULTS AND DISCUSSION ... 20
5.1. Determination of Flow Behavior ... 20
5.2. Temperature Effect on Flow Behavior ... 41
5.3. Impact of Concentration on Flow Behavior ... 45
5.3.1. Sensitivity of Activation Energy to Concentration (Ea) ... 52
5.4. Combined Effects of Temperature, Concentration, and Shear Rate on Flow Behavior ... 53
6. CONCLUSIONS AND RECOMMENDATIONS ... 55
REFERENCES ... 56 CURRICULUM VITAE ... 60 APPENDICES ... 61 APPENDIX A ... 61 Experimental Data ... 61 APPENDIX B ... 81 ANOVA results ... 81 APPENDIX C ... 89 Regression statistics ... 89
IV
SUMMARY
The aim of this study is to determine the rheological properties of some molasses-tahin blends such as date syrup-tahin, mulberry molasses-tahin, grape molasses-tahin and carob syrup-tahin (sesame paste) blends at the different ratios (20 -55 %) and different temperatures (25- 60 °C) by using a rotary viscometer (Brookfield) to develop models appropriate to the experimental data. In order to obtain the viscosities of each blend as a function of the shear strain, those samples were sheared with five different rotational speeds at an increasing order. The variation of viscosity of those blends with the strain rates (2.5-30 s-1) showed that all considered ratios of the molasses-tahin blends were non-Newtonian shear thinning fluids at all temperatures.
The experimental data of apparent viscosity versus shear rate were successfully described with the Power-law model. The model parameters such as the flow behavior index (n) and the consistency coefficient (K) of the considered blends were respectively found to be ranged from 0.522 to 0.641 and from 4365.1 to 10013 mPa.sn for the date molasses- sesame paste blends; from 0.659 to 0.699 and from 4461.1 to 10207 mPa.sn for mulberry molasses- sesame paste blends; from 0.331 to 0.62 and from 966.88 to 4218.2 mPa.sn for grape molasses- sesame paste blends; from 0.444 to 0.599 and from 3194.4 to 17480 mPa.sn for the carob molasses- sesame paste blends. It was observed that apparent viscosities and consistency coefficients of blends increased with increasing molasses concentration and decreasing temperature.
Temperature sensitivity of the consistency index (K) was examined using an Arrhenius-type equation. Activation energies (Ea) of the considered blends were found to be ranged from 4378.15 to 9499 J/mol for the blends of date molasses-sesame paste; from 13216.69 to 7514 J/mol for the blends of mulberry molasses-sesame paste; from 4340.98 to 17378.08 J/mol for the blends of grape molasses-sesame paste; from 6779.04 to 13444.5 J/mol for the blends of carob molasses-sesame paste.
The relationship between concentration and consistency coefficient for each blend was described with both the exponential and power functions. While the exponential function was found to be superior in explaining the variation of Ea with concentrations of date, grape and carob molasses, power function was found to be superior in explaining the variation of Ea with concentration of mulberry molasses.
V
A mathematical model was determined to describe the combined impact of temperature, concentrations of the molasses and shear rate on apparent viscosity with high consistency.
VI
ÖZET
Bazı Pekmez-Tahin Karışımlarının Reolojik Özelliklerinin Modellenmesi
Bu çalışmanın amacı deneysel verilere uyan bir model geliştirmek için farklı konsantrasyon (% 20–55) ve sıcaklıklarda (25–60 C) hurma, dut, üzüm ve keçiboynuzu pekmezleri-tahin gibi bazı pekmez-tahin karışımlarının döner viskozimetre (Brookfield) ile reolojik özelliklerinin belirlenmesidir. Kayma geriliminin fonksiyonu olarak her karışımın viskozitesini elde etmek için bu örnekler artan bir şekilde 5 farklı dönme hızında kayma gerilimine tabi tutuldu. Kayma gerilimleriyle (2.5–30 s-1) karışımların viskozitelerindeki değişim, çalışılan pekmez-tahin karışımlarının bütün sıcaklıklarda Newtonien olmayan kayma incelmeli sıvılar olduğunu gösterdi.
Kayma gerilimlerine karşı görünür viskozitenin deneysel verileri üs kanunu modeli ile başarılı bir şekilde tanımlandı. Çalışılan karışımların akış davranışı indeksi (n) ve kıvamlılık katsayısı (K) gibi model parametreleri sırasıyla; hurma pekmezi-tahin karışımı için 0.522 ile 0.641 ve 4365.1 ile 10013 mPa.sn
, dut pekmezi-tahin karışımı için 0.659 ile 0.699 ve 4461.1 ile 10207 mPa.sn, üzüm pekmezi-tahin karışımı için 0.331 ile 0.62 ve 966.88 ile 4218.2 mPa.sn ve keçiboynuzu pekmezi-tahin karışımı için 0.444 ile 0.599 ve 3194.4 ile 17480 mPa.sn aralıklarında bulundu. Karışımların görünür viskoziteleri ve kıvamlılık katsayıları pekmez konsantrasyonlarının artmasıyla ve sıcaklığın azalmasıyla arttığı gözlendi.
Kıvamlılık katsayılarının sıcaklık duyarlılığı Arrhenius tipi eşitlik kullanılarak incelendi. Çalışılan karışımların aktivasyon enerjisi (Ea); hurma pekmezi-tahin karışımı için 4378.15 ile 9499 J/mol, dut pekmezi-tahin karışımı için 7514 ile 13216.7 J/mol, üzüm pekmezi-tahin karışımı için 4341 ile 17378.08 J/mol ve keçiboynuzu pekmezi-tahin karışımı için 6779.04 ile 13444.5 J/mol arasında bulundu. Her bir karışım için derişim ile kıvamlılık katsayısı arasındaki ilişki hem üstel hem de üs fonksiyonları ile tanımlandı. Ea’nın hurma, üzüm ve keçiboynuzu pekmezlerinin derişimleriyle değişiminin açıklanmasında üstel fonksiyonun daha üstün olduğu bulunurken, Ea’nın dut pekmezi derişimi ile değişimin açıklanmasında üs fonksiyonun daha iyi olduğu bulundu.
Görünür viskozite üzerinde sıcaklık, bazı pekmez derişimleri ve kayma geriliminin birleşik etkisini yüksek tutarlılıkla tanımlama için bir matematiksel model belirlendi.
VII
LIST OF FIGURES
Page No
Figure 2.1 Operations for the production of date molasses ... 4
Figure 2.2 Operations for the production of mulberry molasses ... 5
Figure 2.3 Operations for the production of grape molasses ... 6
Figure 2.4 Operations for the production of carob molasses ... 6
Figure 2.5 Operation for sesame paste production ... 7
Figure 3.1 Rheological behavior of main kinds of liquid. ... 11
Figure 3.2 Time-Dependent Fluids. ... 14
Figure 4.1 Brookfield rotational viscometer. ... 18
Figure 5.1 Change of shear stress with shear rate at various temperatures for a 20 % date molasses in sesame paste ... 20
Figure 5.2 Variation of shear stress with shear rate at various temperatures for a 30 % date molasses in sesame paste ... 21
Figure 5.3 Variation of shear stress with shear rate at various temperatures for a 40 % date molasses in sesame paste ... 21
Figure 5.4 Variation of shear stress with shear rate at various temperatures for a 55 % date molasses in sesame paste ... 22
Figure 5.5 Variation of shear stress with shear rate at various temperatures for a 20 % mulberry molasses in sesame paste ... 22
Figure 5.6 Variation of shear stress with shear rate at various temperatures for a 30 % mulberry molasses in sesame paste ... 23
Figure 5.7 Variation of shear stress with shear rate at various temperatures for a 40 % mulberry molasses in sesame paste ... 23
Figure 5.8 Variation of shear stress with shear rate at various temperatures for a 55 % mulberry molasses in sesame paste ... 24
Figure 5.9 Variation of shear stress with shear rate at various temperatures for a 20 % grape molasses in sesame paste ... 24
Figure 5.10 Variation of shear stress with shear rate at various temperatures for a 30 % grape molasses in sesame paste ... 25
Figure 5.11 Variation of shear stress with shear rate at various temperatures for a 40 % grape molasses in sesame paste ... 25
Figure 5.12 Variation of shear stress with shear rate at various temperatures for a 55 % grape molasses in sesame paste ... 26
Figure 5.13 Variation of shear stress with shear rate at various temperatures for a 20 % carob molasses in sesame paste ... 26
Figure 5.14 Variation of shear stress with shear rate at various temperatures for a 30 % carob molasses in sesame paste ... 27
Figure 5.15 Variation of shear stress with shear rate at various temperatures for a 40 % carob molasses in sesame paste ... 27
VIII
Figure 5.16 Variation of shear stress with shear rate at various temperatures for a 55 % carob molasses in sesame paste ... 28 Figure 5.17 Variation of apparent viscosity with shear rates at different temperatures for a
20 % date molasses in sesame paste ... 28 Figure 5.18 Variation of apparent viscosity with shear rates at different temperatures for a
30 % date molasses in sesame paste ... 29 Figure 5.19 Change of apparent viscosity with shear rates at different temperatures for a 40
% date molasses in sesame paste ... 29 Figure 5.20 Variation of apparent viscosity with shear rates at different temperatures for a
55 % date molasses in sesame paste ... 30 Figure 5.21 Variation of apparent viscosity with shear rates at different temperatures for a
20 % mulberry molasses in sesame paste ... 30 Figure 5.22 Variation of apparent viscosity with shear rates at different temperatures for a
30 % mulberry molasses in sesame paste ... 31 Figure 5.23 Change of apparent viscosity with shear rates at different temperatures for a 40
% mulberry molasses in sesame paste ... 31 Figure 5.24 Variation of apparent viscosity with shear rates at different temperatures for a
55 % mulberry molasses in sesame paste ... 32 Figure 5.25 Variation of apparent viscosity with shear rates at different temperatures for a
20 % grape molasses in sesame paste ... 32 Figure 5.26 Change of apparent viscosity with shear rates at different temperatures for a 30
% grape molasses in sesame paste ... 33 Figure 5.27 Variation of apparent viscosity with shear rates at different temperatures for a
40 % grape molasses in sesame paste ... 33 Figure 5.28 Variation of apparent viscosity with shear rates at different temperatures for a
55 % grape molasses in sesame paste ... 34 Figure 5.29 Variation of apparent viscosity with shear rates at different temperatures for a
20 % carob molasses in sesame paste ... 34 Figure 5.30 Variation of apparent viscosity with shear rates at different temperatures for a
30 % carob molasses in sesame paste ... 35 Figure 5.31 Change of apparent viscosity with shear rates at different temperatures for a 40 % carob molasses in sesame paste ... 35 Figure 5.32 Variation of apparent viscosity with shear rates at different temperatures for a
55 % carob molasses in sesame paste ... 36 Figure 5.33 Temperature effect on consistency coefficient for the various datemolasses
concentrations ... 42 Figure 5.34 Temperature effect on consistency coefficient for the various mulberry
molasses concentrations ... 42 Figure 5.35 Temperature effect on consistency coefficient for the different grape molasses
concentrations ... 43 Figure 5.36 Temperature effect on consistency coefficient for the various carob molasses
IX
Figure 5.37 Relationships between apparent viscosities and shear rates of date
molasses/sesame paste blends at 40°C ... 46 Figure 5.38 Relationships between apparent viscosities and shear rates of mulberry
molasses/sesame paste blends at 40°C ... 46 Figure 5.39 Relationships between apparent viscosities and shear rates of grape
molasses/sesame paste blends at 40°C ... 47 Figure 5.40 Relationships between apparent viscosities and shear rates of carob
molasses/sesame paste blends at 40°C ... 47 Figure 5.41 Relationships of apparent viscosity with shear rate for date, mulberry, grape
and carob molasses/sesame paste blends at 40°C ... 48 Figure 5.42 The influence of date molasses concentration on consistency coefficients at
various temperatures ... 49 Figure 5.43 The effect of mulberry molasses concentration on consistency coefficients at
various temperatures ... 49 Figure 5.44 The influence of grape molasses concentration on consistency coefficients at
different temperatures ... 50 Figure 5.45 The effect of carob molasses concentration on consistency coefficients at
X
LIST OF TABLES
Page No Table 4.1 The composition of molasses used in the experiments ... 17 Table 5.1 Parameters of power-law for the date blends at the various temperatures and
concentrations ... 37 Table 5.2 Parameters of power-law for the mulberry blends at the various temperatures and concentrations ... 37 Table 5.3 Parameters of power-law for the grape blends at the different temperatures and
concentrations ... 38 Table 5.4 Parameters of power-law for the carob blends at the various temperatures and
concentrations ... 38 Table 5.5 Finding of parameters in Eq. (3.8) for the various date molasses concentrations 44 Table 5.6 Finding of parameters in Eq. (3.8) for the various mulberry molasses
concentrations ... 44 Table 5.7 Finding of parameters in Eq. (3.8) for the various grape molasses concentrations
... 44 Table 5.8 Finding of parameters in Eq. (3.8) for the various carob molasses concentrations
... 44 Table 5.9 Finding of parameters in Eq. (3.9) and Eq. (3.10) for various concentrations of
date molasses at the different temperatures ... 51 Table 5.10 Finding of parameters in Eq. (3.9) and Eq. (3.10) for various concentrations of
mulberry molasses at the different temperatures ... 51 Table 5.11 Finding of parameters in Eq. (3.9) and Eq. (3.10) for various concentrations of
grape molasses at the different temperatures ... 51 Table 5.12 Finding of parameters in Eq. (3.9) and Eq. (3.10) for various concentrations of
carob molasses at the different temperatures ... 52 Table 5.13 Determining of parameters in Eq. (3.13) and Eq. (3.14) for various
XI SYMBOLS μ : Newtonian viscosity γ̇ : Shear rate τ0 : yield stress μpl : plastic viscosity K : consistency coefficient n : flow behavior index
μa : apparent viscosity, for power-law fluids μa0 : initial apparent viscosity
μa∞ : equilibrium apparent viscosity
m : the order of the structure breakdown reaction. Equation (3.6) k : the rate constant. Equation (3.6)
t : time of measurement. Equation (3.6) μ0 : experimental constants. Equation (3.7) kt : experimental constants. Equation (3.8) Ea : activation energy (J/mol),
R : universal gas law constant T : absolute temperature (K).
Kc1 : experimental constants. Equation (3.9) Kc2 : experimental constants. Equation (3.10) b1 : experimental constants. Equation (3.9) b2 : experimental constants. Equation (3.10)
K (γ̇, T, C): experimental constants. Equation (3.11 and 3.12) n̄ : average value for flow behavior index. Equation (3.11) b : experimental constants. Equation (3.11 and 3.12) A1 : experimental constants. Equation (3.13)
A2 : experimental constants. Equation (4.14) d1 : experimental constants. Equation (3.13) d2 : experimental constants. Equation (3.14)
C : total soluble solid content. Equation (3.13 and 3.14) Ω :angular velocity (rad/s)
1
1. INTRODUCTION
Molasses-Sesame paste blends is one of a traditional food product in East Asian and Middle Eastern countries. It is mainly consumed for breakfast. Because of it is high-energy content, it has a wide usage specifically in cold weather conditions, such as winter. The constituents of molasses - sesame paste have risen high nutrition value. Usually in markets, molasses and sesame paste are available for sale separately; thus, the blending process is carried out by the consumers. The ratio of molasses to sesame paste is determined according to the consumers taste and preference.
Molasses are commonly produced from grape, mulberry, fig, juniper, watermelon, apple, plum, carob, sugar beet and sugar cane. But in recent years, in addition to those, apricot and date have been used for the production of molasses by concentration of juices up to 70–80% soluble dry matter content with an extended shelf-life (Batu, 2005; Yoğurtçu & Kamışlı, 2006; Akbulut et. al., 2008 ; Karaman & Kayacier,. 2011 ; Özkal & Süren, 2017). Molasses processing operations vary according to origin of fruits used in production of Molasses. (Yoğurtçu & Kamışlı, 2006; Akbulut & Bilgiçli,2010; Karaman & Kayacier,2011).
Sesame paste, known as tahin in Turkey and Arabic countries and ardeh in Iran, is a traditional food in the Middle East, which is produced by grinding the dehulled and heated sesame seeds (Seyed et al.,2007; Gharehyakheh & Tavakolipour, 2014). Sesame paste is also a tradition food in East Asian and Middle Eastern countries, it has used in ingredients of many other dishes such as halawah, chickpeas, desserts, and some types of bakery (Alpaslan & Hayta,2002; Arslan et al.,2005; Akbulut & Özcan,2008; Akbulut et al.,2012).
In addition, the molasses is consumed as an ingredient in the formulation of some food items such as ice cream products, beverages, confectionery, bakery products (Habibi et al., 2006).
Knowledge of rheological behavior is important for optimization of process design, quality control, consumer acceptance of a product and sensory assessment (Arslan et al., 2005; Işıklı & Karababa, 2005; Özkal & Süren, 2017). Consumer acceptance of molasses and sesame paste blends usually depends on the capacity of spreading on other material like bread. Therefore, the spreading of the blends is directly related with viscosity (Alpaslan & Hayta, 2002; Arslan et al., 2005).
2
When the legitimate consistency, soundness and surface tension are the main concerns in expansion, generation and upkeep of the item, the solid rheological information is needed (Abu - Jdayil, 2003; Arslan et al., 2005).
Rheological characterization of food pastes has been widely investigated by focusing at either individual samples or blend samples. Rheological properties of individual samples can be listed as sesame paste (Altay & Ak, 2005 ; Çiftçi et al., 2008; Özkal & Süren, 2017), sunflower tahini (Muresan et al., 2014 ), fenugreek paste (Işikli & Karababa, 2005), tomato paste (Valencia et al.,2002; Bayod et al.,2008), ginger paste (Ahmed, 2004), molasses (pekmez) ( Kaya & Belibaǧlı, 2002; Sengül et al., 2005; Yoğurtçu & Kamışlı, 2006; Sengül et al., 2007; Akbulut et al., 2008; Mohamed & Hassan, 2016). On the other hand, rheological properties of blend samples can be listed as grape pekmez/ tahin blends (Alpaslan & Hayta, 2002; Arslan et al., 2005); corn starch/grape pekmez blends (Goksel et al., 2013), sesame paste/date syrup blends (Habibi et al., 2006; Razavi et al., 2008), honey/sesame paste blends (Gharehyakheh & Tavakolipour, 2013; Gharehyakheh1 et al., 2014) and poppy seed paste/grape pekmez blends (Özkal & Süren,2017).
The flow behavior, texture and sensory properties of new blends need to be determined for processing of those blends. Temperature and concentration are important factors in determining the rheological behavior of the blends. The use of different types of molasses in blending process is an essential component in the formation of a new product accepted by consumers. Some organizations such as military and police organizations required a specific blend ratio. However, much work has been done to improve the quality of food production in terms of edibility taste and texture. It can be obviously seen in the literature that the researchers have focused on blending at different concentrations of sesame paste/grape molasses and sesame paste/dates molasses at different temperature degrees in a hope to improve edibility taste, spread ability on bread and sensory properties etc. Thus, further investigation is required to determine rheological properties of the blends of sesame paste with another type of molasses such as dates, mulberry, grapes and carob juice.
Subsequently, the major objective of this study is to determine rheological behavior of mixtures of sesame paste with different types of molasses such as dates, mulberry, grapes and carob juice.
3
2. OVERVIEW AND LITERATURE SURVEY
2.1. Molasses
Molasses is a concentrated form of dates, mulberry, grapes and carob juice. It is produced by boiled juice to evaporate water without any food additives or sugar. The product can be looked up on natural food, which contains natural sugars with minerals. The goal of concentration or pasteurization is to extend shelf life of dates, mulberry, grapes and carob juices with boiling to lessen water content (Batu, 2005; Yoğurtçu & Kamışlı, 2006; Akbulut et al., 2008; Karaman & Kayacier, 2011; Özkal & Süren, 2017). This process will lead to producing a molasses. Thus, operations for molasses processing vary according to the source of the fruit used in the production of molasses. Some information about the preparation the raw materials such as dates, mulberry, grapes and carob used in production of molasses will be given in the next few paragraphs. The basic operations in molasses productions from the different sources are shown in Figures 2.1 - 2.4. As seen in the figures the process shows small variations according to the type of fruit. The first step in the process for production of molasses from any fruit is to wash the fruit.
2.1.1. Preparation of Date Syrup
As illustrated in Figure 2.1 the shredded samples of the date are heated in suitable amount of water for 20 minutes and mixing. The slurry is filtered. Then, the residue pulp is washed again with hot water (80-85 °C) for 10 minutes to make up the pulp/water ratio as 0.5, 0.4 and 0.3 and then it is filtered again. After that, the collected raw juice is concentrated by using the rotary evaporator apparatus at 70 °C under vacuum. Finally, the produced date syrup is packed and stored at room temperature (20-30 °C) (Ramadan, 1998). Obviously, there are differences between dates and other fruits in producing their juices, other fruit juices are got by pressing (e.g. citrus, berries, grapes), but soluble solids in dates are too concentrated to squeeze (Ramadan, 1998).
4
Figure 2.1 Operations for the production of date molasses
2.1.2. Fresh Mulberry
Fresh mulberry is used as a raw material for the production of mulberry molasses. As can be seen in Figure 2.2, firstly, mulberry placed ships are boiled after washing and then some water is added into it the ratio water to mulberry 0.3-0.4 liter/kg. After that, the mixture is heated about boiling temperature with mixing for about an hour. After that, the mixture is cooled down to about 40-50 ° C. Then, the cold mixture is filtered to obtain clear juice under the pressure. Juice of mulberry is concentrated in open containers by evaporate water, which results in a finished product having 65-72 ° Brix. The final product called mulberry molasses is packaged and stored at room temperature (Basiri, 2016; Sengül et al., 2005).
2.1.3. Fresh Grapes
In the production of grape molasses, (Figure 2.3), the primary step is to wash and smash by utilizing a pneumatic or mechanical press to obtain the grape juice. The obtained grape juice is treated with calcareous soil called molasses earth that contains high amounts of calcium carbonate (ca. 90%).
Dates Washing Crashing (0.5-1
cm) thickness Heating (60 °C) for 20 min Date juice extraction Filtration (coarse and fine) Evaporation ( 70 °C and 500-600 mmHg) Date syrup
5
Figure 2.2 Operations for the production of mulberry molasses
After keeping the earthed juice at the rest for some time, the juice is clarified by sedimentation of calcium tartrat and calcium malate that naturally exist in the form of tartaric and malic acids in the grape juice. Hence, after being decreased acidity, the clear up syrup was boiled in open vessels and seldom in vacuum to take out liquid molasses (Batu, 2005; Hatamikia et al., 2013).
The concentration of grape juice contains a high proportion of mineral, especially calcium and iron. Grape molasses is usually recommended in anemia treatment due to the high iron content (Ozturk & Oner, 1999).
2.1.4. Carob Molasses
As mentioned previously molasses have been produced using various techniques considering species of fruits used in production. In order to obtain carob molasses, the fruits (carob) are smashed into the powdered by using wooden mortar, then added water 1 liter/ kg in an open container during 3 days. After that, the mixture is filtered to obtain carob juice that is concentrated up to 72° Brix in an open vessel with boiling. The final product is known as carob molasses and its color varies between light brown to dark brown depending on the concentration process, (Sengül et al., 2007; Tounsi et al., 2017).
Fresh mulberry Washing Addition of water Mixing and Boiling Cooling at 45-50 °C Transfering into the wooden press Draining Boiling Concentration Liquid mulberry molasses
6
Figure 2.3 Operations for the production of grape molasses
Figure 2.4 Operations for the production of carob molasses
Fresh Grapes Washing Crushing
Pressing Deacidification or neutralization by molasses earth Separation and Clarification Concentration by boiling (65-68°Brix) Grape molasses
Carob (Fruits) Washing Drying Fragmenting
Mixing with water Boiling Juice Boiling until 70 and 80
7
2.2. Sesame Paste
Sesame paste is a final pure product that produced from crushed seeds of sesame (Sesamum indicum L.), which are dehulled and heated without adding or removing any of its components (Alpaslan & Hayta, 2002; Arslan et al., 2005; Gharehyakheh, 2014; Gharehyakheh & Tavakolipour, 2013; Habibi et al. 2006; Razavi et al., 2008). Sesame paste has a high stability and resistance to oxidation at room temperature because of the presence of sesamin and sesaminol that are natural antioxidants (Gharehyakheh & Tavakolipour, 2013; Morris, 2002). It has a significant antioxidant activity due to the main component of sesame oil. The cancer prevention factors, sesamin and sesamolin, are compelling chemicals to smother the arrangement of free radicals hence act as anticarcinogenic materials. Moreover, sesame oil is advantageous for decreasing cholesterol because of its high polyunsaturated fat content (Arslan et al., 2005; Morris, 2002). Besides this, sesame oil can prevent oxidative rancidity due to cancer avoidance factors (Arslan et al., 2005; Jannat et al., 2010).
A typical process of sesame paste production is illustrated in Figure 2.5. The sesame seeds are wetted and then left for 8-10 hours for removing rind process. After the rinds are detached, the seeds are washed for removing any remaining undesirable particles such as stone and dirt. The seeds are centrifuged to remove water, then grilled. The grilled seeds are grinded for obtaining last product, sesame paste. 90 % sesamin, original antioxidant, is discovered after grilling (Arslan et al., 2005; J. Bradley Morris, 2002).
Figure 2.5 Operation for sesame paste production
Sesame seeds Wetting Waiting (8-10 hr) Remove cover Cover separation Washing Dry Roasting Cooling Milling Sesame paste
8
2.3. Molasses/Sesame paste mixtures
Various food products exist in state emulsion such as the mixed salad dressings, sauces, mayonnaise, butter, cream and refreshments. In food system, there are two common types of emulsion, water in oil or oil in water. Blends of molasses and sesame pastes can be regarded as a typical case of an oil-in-water type emulsion (Alpaslan & Hayta, 2002; Arslan et al., 2005). The two non-miscible liquids; molasses and sesame paste form a two-stage system, molasses has water phase (continue stage) and sesame paste has oil phase (dispersed phase). Oil particles are suspended within the water through the assistance of mechanical development of the emulsion (Alpaslan and Hayta, 2002 ; Arslan et al., 2005 ; Seyed et al., 2007).
Emulsion stability depends on oil and water interface. Proteins are amphiphilic molecules that are mostly used to stabilize emulsions in food products. Proteins have a key role to facilitate droplet breakup through homogenization and to stabilize the droplets against coalescence through emulsification and storage. The ability of a protein emulsifier is determined by its ability to reduce tension between the surfaces (Day et al.,2009). In the case of molasses and sesame paste blend, protein and lipids usually interact and thus the protein reduces the tension between surfaces of protein and lipids, which causes a stable emulsion to form (Alpaslan & Hayta, 2002; Arslan et al., 2005).
Sesame paste possesses a high protein and dietary fiber content. When strengthened with high mineral and vitamin being contained in molasses might offer a promising nutritious and healthy substitute to consumers (Alpaslan and Hayta, 2002; Arslan et al., 2005; Çiftçi & Kahyaoglu, 2008).
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3. RHEOLOGY AND FLUID FLOW MODELS
3.1. Rheology
Rheology can be defined as a research of deformation and flow of matter. It is applied to various industrial fields such as mining, geology, cosmetics, and polymers. The biological nature of foods offers an excellent circumstance toward rheological study of fluid foods. An accurate study of the rheological measurement is crucial to tackle the optimization problems in the areas of product development efforts, to design process for processing foods and to improve quality of food product (Heldman & Singh, 1981; Rao, 1999; Vinet & Zhedanov, 2010).
3.2. Importance in the Food Industry
The rheological information is very important in many areas of the food industry assessment such as process design equipments, food texture estimation, shelf life analysis, sensory evaluation and product quality control (Heldman & Singh, 1981; Vinet & Zhedanov, 2010).
3.3. Rheological Behaviors of Fluid Flows
A mathematical equation can be derived from fluid flow behavior that contains rheological information such as viscosity versus shear strain. In addition, it is crucial to specify which model parameters are influenced from the state variables such as temperature and concentration.
In classical mechanics, the difference between liquids and solids is very obvious, as their behaviors are identified using separate physical rules; Hooke’s law and Newton’s law of viscosity. While Hooke’s law defines the solid-state behavior, Newton’s law of viscosity establishes the relationship between shear stress and shear rate for Newtonian fluids. As known solid and fluid materials exhibit different behavior when a stress is applied on them. In this way, the outcome of same amount of stress produces different deformation patterns; the amount of elastic solid deformation is directly proportional to the applied stress, while a fluid deformation continues.
10
A basic distinction between fluid foods is either Newtonian or non-Newtonian behaviors. Fluid foods can be described as either Newtonian or non-Newtonian fluids based on their rheological behavior, whether they follow Newton’s law of viscosity.
3.3.1. Newtonian Fluids
Newtonian fluids can be described as a liquid or gas that comply with Newton’s law of viscosity (Eq.3.1). As mentioned in the previous section, for a perfect Newtonian liquid, the shear stress is linearly proportional to the shear rate (Figure 3.1), with preserving this relationship by a constant value (μ) that is independent of the shear rate (Gankoplis, 1993).
In this case, when plotting shear stress versus shear strain, the curve starts from the origin and the slope of curve (μ) stays constant. Let us denote the force as N, area as m2, length as m, and final velocity as m/s.
τ = μ ⋅γ̇ (3.1)
Here τ is the shear stress, μ is the Newtonian viscosity and γ̇ is the shear rate. A common Newtonian food can be defined as compounds of low molecular weight with low concentrations. Such as water, sugar syrups, and milk (Intergovernmental Panel on Climate Change, 1999).
3.3.2. Non-Newtonian Fluids
The fluids belonging non-Newtonian types are those which do not obey Newtonian’s law of viscosity and this can be observed by focusing on the relationship between shear stress with shear rate. The curve for shear stress versus shear strain is nonlinear and does not begin from origin.
Dispersions, emulsions, and polymer solutions can be counted as typical non-Newtonian materials. The viscosity is not constant, but is a function of shear rate and appears as either a time-dependent or independent. Time-independent flow behavior does not rely on duration of shear but only on shear rate while time-dependent flow behavior relies on the duration of shear.
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Figure 3.1 Rheological behavior of main kinds of liquid
3.3.2.1. Time Independent Fluids
Bingham Plastics
The behavior of this type of fluid is the closest to the Newtonian behavior and the relationship between shear stress and shear rate is linear, only difference is that the curve of this type of fluid does not begin from the origin (see Figure 3.1) (Vinet & Zhedanov, 2010). The relationship between shear stress and shear rate is given as follows:
τ = μpl γ̇ + τ0 (3.2)
where τ0 is the yield stress and μpl is the plastic viscosity. Yield stress (τ0) is required to stat flow. Underneath the yield stress, no flow occurs and the material exhibits solid like characteristics due to the stored energy (Vinet & Zhedanov, 2010).
Power-law Fluids
The behavior of this sort of liquid has a place in non-Newtonian behavior; they can be characterized by an Ostwald de Waele (or Power-law model) equation. It is demonstrated that Power-law model has been utilized broadly to clarify flow behavior of non-Newtonian fluids, in both hypothetical examination and observational calculations (Fung, 1982; Vinet & Zhedanov, 2011)
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τ = K ⋅γ̇n (3.3)
where, K (Pa. sⁿ) is consistency coefficient, n is flow behavior index, dimensionless. The consistency coefficient is very important to identify the viscous nature of a liquid.
Apparent viscosity can be well defined by the ratio of shear stress to shear rate; this ratio is not a constant but relies on the shear rate. In other words, the apparent viscosity represents the non-Newtonian viscosity (Van Wazer & Lyons, 1966). The apparent viscosity (μa) for Power-law fluids (Vinet & Zhedanov, 2010) is given as:
µₐ = f(γ̇) = (K.γ ̇ⁿ
γ̇ ) = K. γ̇
n−1 (3.4a)
of which the logarithmic frame is utilized to obtain its parameters such as the consistency coefficient and flow behavior index when exploratory information is accessible as,
lna = lnK + (n −1) lnγ̇ (3.4b)
Flow behavior index, n, is effect on power law fluids that is classified into two types such as shear thinning fluid and shear thickening fluid.
Shear Thinning (or pseudo plastic) Fluids
This type of non-Newtonian fluids is more encountered than other types. In this type of fluid, the plotted curve for the shear stress versus shear rate is concave upward and it begins at the origin (Figure 3.1). An increase in shear stress gives less than equal increments in the shear rate. Apparent viscosity decreases with increasing shear rate in shear thinning fluids whilst it is constant with Newtonian fluids. If Eq. (3.3) is assigned to this sort of behavior, it will be seen that the flow behavior index is less than unity (n <1) (Heldman & Singh, 1981; Rao, 1999; Vinet & Zhedanov, 2010). Orange juice concentrate, banana puree, many salad dressings and applesauce exhibit shear thinning fluid behaviors (or pseudo plastic).
13 Shear Thickening (or Dilatant) Fluids
In Dilatant (or shear thickening) behavior, the plotted curve for the shear stresses versus shear rates in this sort of liquid is concave descending and it moreover starts at the origin point (see Figure 3.1). Apparent viscosity is the slope of the related curve and depends upon the shear rate. This sort of flow is watched with gelatinized starch dispersion and corn flour-sugar arrangements (Rao, 1999). Model equation of Power law (Eq.3.3) is often proper with the flow behavior index more than unity (n >1).
Herschel - Bulkley Fluids
Herschel- Bulkley (or Pseudoplastic) model can be counted as a common relation to characterize the behavior of non-Newtonian liquids.
τ = K. γ̇n+ τ0 (3.5)
It is more general equation since it reduces to the power law fluid (n ≠ 1) and to Newtonian fluid (n = 1) as extraordinary cases (τ0 = 0). Moreover, it is suitable for the Bingham Plastic fluid where the yield stress is required (Vinet & Zhedanov, 2011).
3.3.2.2. Time-Dependent Fluids
The reversible or irreversible changes take place according to increase or decrease of apparent viscosity with time at a constant shear rate. Time dependent fluids can be examined by dividing into two subtitles namely thixotropic and rheopectic fluids.
Thixotropic Fluids
Thixotropic fluids are known as shear thinning behavior, dependent on time (see Figure 3.2). The majority of these fluids have a heterogeneous system consist of an excellent dispersed phase. When at rest, particles and molecules in the food are linked together by weak forces. During shear the hydrodynamic forces are sufficiently high to break the
14
interparticle linkages, resulting in a reduction in the size of structural units. Hence, a lower resistance during the fluid flow is seen at amid shear rates.
Figure 3.2 Time-dependent fluids
This sort of stream behavior is likely seen with nourishments, for instance serving of mixed salad dressing and delicate cheeses where the structural changes take put within the nourishment until stability is satisfied (Rao, 1999). The event of thixotropy suggests that the flow history needs to be considered if the liquid behavior is foreseen (Singh, 2001).
Sesame paste was considered to show the thixotropic behavior by Abu - Jdayil (2003). The auxiliary breakdown of sesame oil at a consistent shear rate was expressed by,
(μa−μa∞
μa0−μa∞) 1−m
= (m − 1)kt + 1 (3.6)
where, initial apparent viscosity is μa0, equilibrium apparent viscosity is μa∞, the structure breakdown response is m, rate constant is k and time of estimation is t.
Rheopectic Fluids
Rheopexy fluids are known as shear thickening behavior, dependent on time (see Figure 3.2). The viscosity of these foods at a constant shear rate increases with time (Vinet & Zhedanov, 2010).
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3.4. Effective Variables on Viscosity
The viscosity of a fluid depends on many factors such as temperature, concentration, shear rate time of shearing and pressure. Because of the changes in these variables, liquids are subjected to high affectability. In turn, these variables affect viscosity because of the resulting structural changes in the fluid. Although the effect of pressure is ignored for most practical purposes, the effect of temperature and concentration are obvious on the fluid behaviors (Singh, 2001).
Effect of Temperature
Temperature usually has an inverse relationship with viscosity. During preparing and storing of liquid nourishments, a massive range of temperatures are encountered. The role of temperature on viscosity is clarified by Arrhenius type equation (Rao, 1999; Singh, 2001) that is given as:
µₐ = µ0. e[R.TEa] (3.7)
K = Kt. e[
Ea
R.T] (3.8)
where, μ0 and Kt constants, Ea is the activation energy, R is the universal gas constant and T is the absolute temperature
Effect of Concentration
Concentration of a solute has, as a rule feature, a nonlinear relationship with viscosity at a constant temperature (Vinet & Zhedanov, 2010). It is essential to distinguish the components that play a crucial role on the rheological behavior. Hence, the impact of concentration on viscosity is expressed by either exponential or power functions (Rao, 1999) as follows:
K = Kc1. eb1.C (3.9)
K = Kc2. Cb2 (3.10)
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The Combined Effect of Temperature and Concentration
The viscosity of a fluid food increase with a decrease in temperature and an increase in concentration. The combination factor of temperature and concentration are well described with shear rate. In other word the combined effects of temperature, concentration and shear rate on the apparent viscosity is expressed with the exponential and power function as follow: µₐ = f(𝛾̇, c, т) = K(γ̇, c, т) exp [Ea R . ( 1 T) + b. C] . γ̇ n̄−1 (3.11) or: µₐ = f(c, т) = K(c, т) exp (Ea R.T) . C b. γ̇n̄−1 (3.12)
where, K (T, C, γ̇) is empirical constant, and n̄ is a moderate value for stream behavior index (Vinet & Zhedanov, 2010).
3.5. Impact of Concentration on Activation Energy
The soluble solid content of food is a significant function for activation energy at a certain temperature. The exponential or power functions are utilized to express concentration effect on activation energy.
Ea = A1. ed1.C (3.13)
Ea = A2. Cd2 (3.14)
where, A1, A2, d1, d2 are empirical constants and C is solid content in the mixture (Kaya and Belibaǧlı, 2002).
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4. MATERIALS AND METHODS
4.1. Materials
The composition of sesame paste (tahin) bought from Merter Helva San. ve Tic. A.Ş., Istanbul was 60.2 % total fat, 9.7 % carbohydrate, and 26 % protein. °Brix values for date, mulberry, grape and carob were 73. 68.75, 60.56 and 77.5 respectively.
Brix level of each commercial molasses, soluble solid content, was determined by using a refractometer (METTLER TOLEDO RE50, Switzerland) in the local sugar beet processing plant (Elazığ Şeker Fabrikası).
Table 4.1 The composition of molasses used in the experiments
Types Composition Dates Molasses Mulberry Molasses Grapes Molasses Carob Molasses Total carbohydrate (%) 77 73 64.1 66.95 Protein (%) 0. 1 2.4 1.9 2 Brix 73 68.75 60.56 77.35
To accurate viscosity estimation, samples ought to be free from entrapped air (air bubbles); for this reason, the homogeneous blends of molasses and sesame paste are rested at room temperature for 5 hours.
4.1.1. Preparation of Same Molasses/Sesame Paste Blends
After making sure the samples free from entrapped air or air bubbles, the molasses-sesame paste blends such as blends of date syrup- molasses-sesame paste, mulberry molasses-molasses-sesame paste, grape molasses-sesame paste and carob syrup-sesame paste (tahin) at the different weight ratios (20 %, 30 %, 30 % and 55 %) (wt./wt.) were sheared under different shear strains to measure viscosities of those blends. In order to prepare a homogenous blend, the mixtures were blended consistently with a spatula. The blends were rested for 5 hours before subjecting to the rheological measurements.
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Figure 4.1 Brookfield rotational viscometer
The viscosity for each blend was measured at various temperatures (25, 30, 40, 50 and 60 °C) by using a rotary Viscometer (Brookfield). In order to obtain the viscosities of each blend as a function of the shear strain, those specimens were sheared with a few distinctive rotational speeds at a rising arrange.
4.2. Rheological Analysis
4.2.1. Measuring of Rheological Behavior
Brookfield rotational viscometer (Model DV-II, Brookfield Engineering Laboratories) was utilized to measure viscosities of the blends by using spindle 28 and the sample cup with 12 ml sample volume was at different temperature and concentration.
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For obtaining the rheograms for each blend, the shear stress and viscosity were directly read from the viscometer for each shear rate in ranges of 2.5 to 30 rpm.
The rheological measurements of some ratios of the molasses-sesame paste mixtures with changing molasses contents of 20 %, 30 %, 40 % and 55 % (wt./wt.) were studied at different temperatures of 25, 30, 40, 50 and 60 °C. For all experiment, data collection for each specimen was finished after 5 revolutions at a set rotational speed. At that point for each progressive revolution, one point of viscosity and shear stress information on the set rotational speeds was recorded up to 5 values.
4.2.2. Statistical Analysis
Rheological properties and flow behavior of some ratios of the molasses-sesame paste mixes were evaluated by applying the linear regression method via Microsoft Excel software. The utilized equations and coefficient of determination (R²) were detailed. Analysis of variance (ANOVA) test was approved to recognize any noteworthy contrast, among theoretical parameters; n and K beneath the temperature impact and molasses concentration impact (α = 0.05). Factors of temperature, concentration, and shear rate were combined into a single logarithmic model by utilizing multiple linear regression system with using lines function in Microsoft Excel Software.
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5. RESULTS AND DISCUSSION
5.1. Determination of Flow Behavior
In order to evaluate the rheological behavior of some molasses/sesame paste blends at different concentrations of molasses and temperatures, the blends were prepared by adding molasses into the sesame paste in ratios of 20-55% (wt. /wt.). During the measurement of viscosity of each blend, the temperatures were varied from 25 °C to 60 °C for each concentration and each shear rate. Five different rotational speeds were set to measure viscosity and shear stress for each blend.
By considering the relationship between shear stress and shear rate at each temperature and concentrations, all experimental results indicated that the blends are Power-law type shear thinning non-Newtonian fluids. Figures 5.1 to 5.16 illustrated the variation of measured shear stress with the shear rate of the considered blends at different temperatures and concentrations of molasses. The measured apparent viscosities of the blends versus shear rates are depicted in Figures 5.17 – 5.32. As can be seen in the figures the apparent viscosities decrease with increasing shear rates, which means the blends in question exhibit shear thinning behavior.
Figure 5.1 Change of shear stress with shear rate at various temperatures for a 20 % date molasses in sesame paste
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Figure 5.2 Variation of shear stress with shear rate at various temperatures for a 30 % date molasses in sesame paste
.
Figure 5.3 Variation of shear stress with shear rate at various temperatures for a 40 % date molasses in sesame paste 0 10 20 30 40 50 60 70 80 90 0 2 4 6 8 10 S he ar stre ss x 10¯²( mP a ) Shear rate (1/s) C=40% date
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Figure 5.4 Variation of shear stress with shear rate at various temperatures for a 55 % date molasses in sesame paste
Figure 5.5 Variation of shear stress with shear rate at various temperatures for a 20 % mulberry molasses in sesame paste
23
Figure 5.6 Variation of shear stress with shear rate at various temperatures for a 30 % mulberry molasses in sesame paste
Figure 5.7 Variation of shear stress with shear rate at various temperatures for a 40 % mulberry molasses in sesame paste
24
Figure 5.8 Variation of shear stress with shear rate at various temperatures for a 55 % mulberry molasses in sesame paste
Figure 5.9 Variation of shear stress with shear rate at various temperatures for a 20 % grape molasses in sesame paste
25
Figure 5.10 Variation of shear stress with shear rate at various temperatures for a 30 % grape molasses in sesame paste
Figure 5.11 Variation of shear stress with shear rate at various temperatures for a 40 % grape molasses in sesame paste
26
Figure 5.12 Variation of shear stress with shear rate at various temperatures for a 55 % grape molasses in sesame paste
Figure 5.13 Variation of shear stress with shear rate at various temperatures for a 20 % carob molasses in sesame paste
27
Figure 5.14 Variation of shear stress with shear rate at various temperatures for a 30 % carob molasses in sesame paste
Figure 5.15 Variation of shear stress with shear rate at various temperatures for a 40 % carob molasses in sesame paste
28
Figure 5.16 Variation of shear stress with shear rate at various temperatures for a 55 % carob molasses in sesame paste
Figure 5.17 Variation of apparent viscosity with shear rates at different temperatures for a 20 % date molasses in sesame paste
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Figure 5.18 Variation of apparent viscosity with shear rates at different temperatures for a 30 % date molasses in sesame paste
Figure 5.19 Change of apparent viscosity with shear rates at different temperatures for a 40 % date molasses in sesame paste
30
Figure 5.20 Variation of apparent viscosity with shear rates at different temperatures for a 55 % date molasses in sesame paste
Figure 5.21 Variation of apparent viscosity with shear rates at different temperatures for a 20 % mulberry molasses in sesame paste
31
Figure 5.22 Variation of apparent viscosity with shear rates at different temperatures for a 30 % mulberry molasses in sesame paste
Figure 5.23 Change of apparent viscosity with shear rates at different temperatures for a 40 % mulberry molasses in sesame paste
32
Figure 5.24 Variation of apparent viscosity with shear rates at different temperatures for a 55 % mulberry molasses in sesame paste
Figure 5.25 Variation of apparent viscosity with shear rates at different temperatures for a 20 % grape molasses in sesame paste
0 2000 4000 6000 8000 10000 12000 0 1 2 3 4 5 6 7 8 9 A ppar ent v isc osi ty ( m Pa.s) Shear rate (1/s) C=55% mulberry 0 500 1000 1500 2000 2500 3000 0 2 4 6 8 10 A ppar ent v isc osi ty ( m Pa.s) Shear rate (1/s) C=20% grape
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Figure 5.26 Change of apparent viscosity with shear rates at different temperatures for a 30 % grape molasses in sesame paste
Figure 5.27 Variation of apparent viscosity with shear rates at different temperatures for a 40 % grape molasses in sesame paste
0 500 1000 1500 2000 2500 3000 3500 4000 0 2 4 6 8 10 A ppar ent v isc osi ty ( m Pa.s) Shear rate (1/s) C=30% grape
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Figure 5.28 Variation of apparent viscosity with shear rates at different temperatures for a 55 % grape molasses in sesame paste
Figure 5.29 Variation of apparent viscosity with shear rates at different temperatures for a 20 % carob molasses in sesame paste
35
Figure 5.30 Variation of apparent viscosity with shear rates at different temperatures for a 30 % carob molasses in sesame paste
Figure 5.31 Change of apparent viscosity with shear rates at different temperatures for a 40 % carob molasses in sesame paste 0 2000 4000 6000 8000 10000 12000 14000 0 2 4 6 8 10 A ppar ent v isc osi ty ( m Pa.s) Shear rate (1/s) C=40% carob
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Figure 5.32 Variation of apparent viscosity with shear rates at different temperatures for a 55 % carob molasses in sesame paste
The model parameters such as the consistency coefficient and the flow behavior index can be determined by regression analysis based on the achieved results. According to the experimental finding, viscosities as a function of shear rates were finely fitted with Eq. (3.4b) to determine the model parameters; where the slope of regression line represents a flow behavior index, n, and the intercept of the graph shows the consistency coefficient, K. Table 5.1 to 5.4 includes the values of n, K and the coefficient of determination, R2 for the considered blends at the specified concentrations and temperatures. In fact, the values of each type of blend given in Table 5.1 to 5.4 were obtained from each curve equation in Figure 5.17 – 5.32 at the specified concentrations and temperatures. The equation for each curve in the figures were found to be in a power function since the equation for the best fitting curve to the experimental data were found to be in a general form of 𝑦 = 𝑎𝑥𝑏.
The corrections were applied to the shear rate of the experimental data. Power-law approximation method was implemented for the corrections of Newtonian shear rates. The average correction has been calculated for the consistency coefficient, and flow behavior index, were found to be near 7 % for date, 9 % for mulberry, 4.6 % for grape and 5.4 % for carob of data. The correction values also consistent with the error in the theoretical percentage might produce from the use of the Newtonian approximation instead of power-law approximation.
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Table 5.1 Parameters of power-law for the date blends at the various temperatures and concentrations
Table 5.2 Parameters of power-law for the mulberry blends at the various temperatures and concentrations date
20 % 30 % 40 % 55 %
T(˚C) n K(mPa.sn) R² n K(mPa.sn) R² n K(mPa.sn) R² n K(mPa.sn) R²
25 0.617 6626.9 0.9855 0.538 8113.3 0.9897 0.629 9719.3 0.9878 0.639 10013 0.9927 30 0.585 6166.3 0.9914 0.532 7505.5 0.9901 0.612 9468.6 0.9908 0.641 9704 0.9888 40 0.569 5315 0.9948 0.536 6798.7 0.9976 0.607 8712.6 0.9984 0.629 9231.4 0.9892 50 0.544 5013.1 0.9924 0.535 6308.8 0.9982 0.594 8014.5 0.9939 0.606 8813.1 0.9753 60 0.532 4365.1 0.991 0.522 5744.7 0.9903 0.595 7664.6 0.9988 0.573 8269.7 0.9942 mulberry 20 % 30 % 40 % 55 %
T(˚C) n K(mPa.sn) R² n K(mPa.sn) R² n K(mPa.sn) R² n K(mPa.sn) R²
25 0.659 7714 0.9977 0.698 8057.4 0.9972 0.699 8597.7 0.9755 0.69 10207 0.9953
30 0.691 6868.1 0.9942 0.69 7165.5 0.979 0.683 7769.1 0.9846 0.682 9401 0.9844
40 0.690 5753.2 0.9837 0.69 6311.9 0.9862 0.68 6981.9 0.9917 0.676 8418.7 0.9732
50 0.689 4809.9 0.9648 0.679 5513.6 0.9689 0.679 6168.7 0.99 0.674 7905.6 0.987
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Table 5.3 Parameters of power-law for the grape blends at the different temperatures and concentrations
Table 5.4 Parameters of power-law for the carob blends at the various temperatures and concentrations grape
20 % 30 % 40 % 55 %
T(˚C) n K(mPa.sn) R² n K(mPa.sn) R² n K(mPa.sn) R² n K(mPa.sn) R²
25 0.604 2084.5 0.9715 0.525 2906.5 0.9927 0.512 3254.4 0.9964 0.496 4218.2 0.9931 30 0.579 1647.4 0.9886 0.508 2421.8 0.9945 0.462 3033.4 0.9953 0.46 4100.6 0.9982 40 0.546 1300.1 0.9869 0.456 2232.7 0.9976 0.62 2782.3 0.9943 0.461 3809.7 0.9984 50 0.515 1113.7 0.9899 0.418 2033.9 0.9971 0.382 2582 0.9942 0.389 3709.5 0.9976 60 0.511 966.88 0.9928 0.374 1876.5 0.9985 0.331 2446.5 0.9986 0.336 3496.6 0.986 carob 20 % 30 % 40 % 55 %
T(˚C) n K(mPa.sn) R² n K(mPa.sn) R² n K(mPa.sn) R² n K(mPa.sn) R²
25 0.583 5714.8 0.9963 0.599 7001.6 0.9964 0.547 11290 0.9982 0.546 17480 0.9853 30 0.534 5123.2 0.9881 0.558 6007.1 0.9667 0.556 10671 0.9933 0.527 15808 0.9905 40 0.460 4515.9 0.991 0.492 5769.1 0.9847 0.562 9176.6 0.9838 0.528 14660 0.9876 50 0.447 3762.7 0.9949 0.485 4894.4 0.9926 0.529 8390.3 0.9964 0.475 13479 0.9813 60 0.444 3194.4 0.9981 0.476 4397 0.9978 0.528 8213.7 0.9963 0.451 12990 0.996
39 %Error = 1 − [shear rate of newtonian
shear rate of power ֗] (5.1) Newton shear rates and non-Newton shear rate were computed by following equations.
𝛾̇ь = 2. 𝛺. [ 𝛼2 𝛼2−1] (5.2) γ̇ь = (2Ω n) [ α 2 n α 2 n−1 ] (5.3)
The obtained model parameters namely flow behavior index and consistency coefficient in the range of the determination coefficient (R2) indicate that the Power- law model seems to be convenient to describe the flow behavior of mixtures. The ranges of these model parameters for date, mulberry, grape, and carob molasses are shown in Tables 5.1, 5.2, 5.3, and 5.4 respectively. For the date molasses range correlation coefficient (R2) between 0.9753 – 0 .9988, for the flow behavior index (n) is in 0.522 – 0.641 and for the consistency coefficient (K) is in 4365.1 – 10013 mPa.sn. For the mulberry molasses range correlation coefficient (R2) between 0.9977 – 0.9648), for the flow behavior index is in 0.659 – 0.699 and for the consistency coefficient is 4461.1 – 10207 mPa.sn. For the grape molasses range correlation coefficient (R2) between 0.9986 – 0.9715, for the flow behavior index is in 0.331 – 0.62 and for the consistency coefficient is in 966.88 – 4218.2 mPa.sn. For the carob molasses range correlation coefficient (R2) between 0.9986 – 0.9667, for the flow behavior index is in 0.444 – 0.599 and for the consistency coefficient is in 3194.4 – 17480 mPa.sn.
In all cases, it can be noticed that the determination coefficient (R2) is higher than 0.85 and the flow behavior index are smaller than unity (n < 1) that means all blends exhibit the shear-thinning (pseudo plastic) behavior since pseudo plasticity is inversely proportional to the flow behavior index (Grigelmo et al., 1999; Arslan et al., 2005).
The major constituents of sesame paste are protein and oil whereas molasses components are mainly sugar and water. The decrease in an apparent viscosity with increasing shear rate is often explained with changing in the structure of the mixture since the uniformity level of those constituent particles increases with the hydrodynamic forces (Alparslan and Hayta, 2002; Rao, 1999). The effect of shear produced from the structural change on the oil droplet
40
has been stated to egg yolk stabilized mixtures by Moros et al. (2002). More specifically, shearing leads to a gradual deformation and disruption of the oil droplets, which results in less resistance for fluid flow (Singh et al., 2003).
Yoğurtçu & Kamışlı, (2006) showed that the different molasses (grape, mulberry, harnup juice, and rosehip) exhibit non-Newtonian behaviors. The viscosities of those samples decrease with increasing shear rate as in pseudo plactic fluids. Also, Kaya & Belibağlı (2002) illustrated that molasses samples with the range of 52.1- 72.9 °Brix possess Newtonian fluid behaviors.
On the other hand, Abu- Jdayil, et al., (2002) and Abu-Jdayil ( 2003) reported that the sesame paste exhibits thixotropic behavior. By considering, thixotropic sesame paste blended with Newtonian molasses at concentrations of 20-55 %, it can be said that the time reliance of sesame paste is likely compensated by molasses at the taken a toll of losing its Newtonian behavior. Subsequently, the detected shear thinning behavior of the mixes shows up to be a center property between both unmistakable stream behaviors (Newtonian molasses and non-Newtonian sesame paste). This explanation was backed by the empirical estimations of the apparent viscosity of molasses/sesame paste mixes at a consistent shear rate, which is uncovered no discernible alteration with time.
According to the studies of Alparslan & Hayta (2002), Arslan et al., (2005); Habibi et al., (2006) and Razavi et al., (2008), the molasses/sesame paste blends display non-Newtonian, shear thinning behavior
Alparslan & Hayta (2002) reported that all blends of sesame paste/molasses mixtures having a molasses concentration range of 2- 6% (wt./wt.) at the temperature variances of 30- 75 °C exhibit pseudo plastic behavior.
Arslan et al., (2005) reported that sesame paste/molasses blends having sesame paste concentrations (20-32%) and the temperature variations of (35-65 °C) display non- Newtonian, shear thinning behavior.
The date syrup /sesame paste blends, date molasses having variety solid contents of 60 and 65 °Brix, at the temperature ranges of 25-55 °C exhibit pseudo plastic behavior (Habibi et al., 2006).
Razavi et al., (2007) studied on the flow behavior of the sesame paste/date syrup mixtures at reduced fat of three different concentrations that are xanthan gum (0.0 1, 0.015, and 0.02 %
